Since neural cells have been used as a candidate material for treatment of cranial nerve diseases such as Alzheimer's disease, depression, Parkinson's disease, cerebral infarction, cerebral hemorrhage, spinal cord injury, etc., extensive research related to neural cells has recently been actively conducted, and a number of papers and patens have been disclosed. However, the neural cells or neural stem cells are difficult to obtain, and thus many studies related to differentiation of mesenchymal stem cells, which are relatively easy to obtain, into neural cells have been conducted. According to Lauren's review paper (Plast. Reconstr. Surg. 116:1453, 2005), among six reports on differentiation of fat-derived mesenchymal stem cells into neural cells in vitro by a chemical method, differentiated neural cells exhibiting functionally significant electrophysiological properties have been reported in one case. According to Arshak (Stem Cells and Development, 17: 1123-30, 2008), the differentiation of bone marrow-derived mesenchymal stem cells into neural cells was induced by chemical differentiation, and differentiated neuronal markers were investigated by immunohistochemistry, Western blot (B3T, GFAP, MAP-2, NeuN), ELISA (nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF)), etc. to observe their properties, but the electrophysiological properties were not found. Research aimed at using mesenchymal stem cells in neurological treatment by mixed culture of neural cells or neural precursor cells has been conducted (Croft A P, Exp. Neurol., 216(2): 329-41 (2009)), but it is practically impossible to obtain a sufficient amount of human neural cells or neural precursor cells used in the mixed culture. As another research direction, a study of inducing overexpression of neuronal genes using lentivirus to improve the differentiation has been conducted (Watson, D. J., Journal of Neurotrauma, 21:1723-36. (2004), Hofstetter, C., Nature Neuroscience, 8: 346-53. (2005)), but the safety of the virus has not been ensured, which makes it difficult to apply to cell therapy.
According to Kuh et al. (Acta Neurochir 147:985-992, 2005), at 8 weeks after transplantation of human umbilical cord blood cells into mice with spinal cord injuries, similar results were observed in Basso, Beattie and Bresnahan (BBB) scores compared with the control group with media alone, and at 5 weeks after transplantation of human umbilical cord blood cells mixed with brain-derived neurotrophic factor (BDNF), similar results were obtained, from which it can be seen that the simple transplantation of stem cells has limitations. According to Rooney et al. (Tissue Engineering Part A, Mar. 31, 2009), after transplantation of glial cell line-derived neurotrophic factor (GDNF) genes into bone marrow-derived mesenchymal stem cells isolated from fluorescent protein mice, it was observed that the stem cells into which the glial cell line-derived neurotrophic factor genes were introduced survived for 6 weeks. However, after transplantation of mesenchymal stem cells alone, the transplanted cells were not observed after 2 weeks, and thus it was reported that the transplantation of mesenchymal stem cells alone was insufficient for the treatment of spinal cord injuries.
One known neurological treatment technique using waves includes a system for applying a low-frequency of approximately 10 Hz to a patient's brain tissue, in which direct electrical stimulation is applied to electrodes implanted in or on the patient's brain to cause a magnetic field due to electrical currents (US20060205993). Zheng discloses a magnetic stimulation apparatus for central nervous system, in which the magnetic stimulation with a precise wave form, high frequency or a combination of a plurality of frequency components is used for improvement of brain function (JP2008-543388). Riken discloses a method for preparing neural cells by electric pulse treatment of embryonic stem cells (US20070065941). Gliner et al. disclose a method for preparing neural cells by electric pulse treatment of cells (US20050075679). However, the above techniques employ direct implantation of electrodes, which involve electrode implant surgery that causes pain to patients. In the case of embryonic stem cells, the possibility of tumor formation is raised, and there are limitations in their application to clinical trials.
Accordingly, an effective method that can differentiate mesenchymal stem cells, which are easy to obtain, into neural precursor cells, is urgently required.